Find the Key of the Numbers — Python

# Time:  O(d), d = 4
# Space: O(1)

# math
class Solution(object):
    def generateKey(self, num1, num2, num3):
        """
        :type num1: int
        :type num2: int
        :type num3: int
        :rtype: int
        """
        L = 4
        result = 0
        base = pow(10, L-1)
        for _ in xrange(L):
            result = result*10+min(num1//base%10, num2//base%10, num3//base%10)
            base //= 10
        return result